Resting on observations on China's diplomatic behavior with North Korea, a theory can be entertained to state that China may regard North Korea as an unspoken "core interest." If this theory holds ground, then it would indicate that Donald Trump's ongoing artful deal-making outreach to Xi Jinping, so as to invite Xi to serve as a "hitman" on Pyongyang, is bound not to materialize. The extended larger implications may be profoundly disturbing for the future of a Sino-U.S. strategic relationship.

According to the Chinese Communist Party (CCP), "core interest" is the highest level of national interest among the three interests (core, major and general). It is so important that there can be "no room for compromise" (burong tuoxie). As a reference, nowadays Xi is also officially called the "core" leader to signify his absolute grip on power.

A notable feature of China's "core-interest" concept is that the list is expanding. In addition, not all things on this list are made public for strategic reasons. For instance, in 2010, China included the South China Sea as its "core interest." Since then, China has never compromised on its claim to the sea, despite having to shoulder wide international criticism.

A caveat is that the core-interest concept generally applies to China's claims of territory and sovereignty. North Korea as a state therefore is outside the core-interest category. However, China has been increasingly flexible in exploiting the concept to suit its expanding interests. In addition, there is no modus-operandi consensus among Chinese scholars on what constitutes its core interests.

To sum up, if North Korea is not a Chinese core interest, then it may not be as important to China as many outsiders believe. If so, China might also opt for abandonment or negligence. However, what is interesting is that throughout its history, Beijing has never abandoned Pyongyang, nor has it yielded its influence to another regional hegemon.

For instance, during the Japanese invasion of Korea in the Imjin War (1592–98), China sent troops, calling for "Resist Japan, Help Korea." During the Korean War (1950-53), China again sent troops, calling for "Resist America, help Korea." This reflects the old Chinese empire's tendency to regard Korea as belonging within the Chinese sphere of influence.

Of particular note is that Xi as vice president in 2010 called the Chinese intervention into the Korean War as a "just war" against American aggression. When his remarks generated cacophony among neighboring countries, including South Korea, the Chinese foreign ministry defended Xi's remarks, saying they reflected the CCP's official view. Today, with South Korea being a U.S. ally, and amid the deepening Sino-U.S. rivalry and competition, China may even further quietly and tacitly regard the North as a strategic asset, not a liability, to counter U.S. clout in the region.

Against this backdrop, it may be argued that North Korea is China's unspoken core interest. China enjoys the flexibility of ambiguity and does not have to articulate its relationship with the North. It is Chinese actions that speak.

To test this theory, during the heyday of the anti-North Korean sentiment in China in 2013 (after Pyongyang staged a third nuclear test near the Chinese border that sparked school evacuations and Chinese citizens' protests in front of North Korean missions), this writer raised the idea of China increasingly seeing Pyongyang as a problem that could be abandoned.

To the question, a senior editorial writer for a Chinese state-run newspaper smiled and said: "Xiang dou bu yao xiang" (Don't even think about it!).

If for China, North Korea's collapse or implosion or regime change or a "preemptive strike" by the U.S. is beyond its tolerance threshold, then Trump will realize, sooner or later, that his placing hope on China in exerting "total control" (in his own words) over North Korea is a bad bet.

China may also not be able to tolerate the deployment of THAAD because it sees the U.S. as the major existential threat, while Pyongyang's various belligerent acts are a mere "inconvenience."

The extended larger implication may be profoundly disturbing: the very reason China cannot fully partner with the U.S. and give up on North Korea, is America itself because China sees it as the primary existential threat. This idea is still hypothetical but may deserve to be tested.

Lee Seong-hyon, Ph.D., is a research fellow at the Sejong Institute. Reach him at sunnybbsfs@gmail.com